#### Answer

The correct answer is: (c)

#### Work Step by Step

The correct answer is: (c)
On the $v_x$ versus time graph, the slope of the graph represents the acceleration $a_x$. Graph (a), graph (b), and graph (d) all show an acceleration that is constant. Graph (c) has a slope that is changing but always positive. Note that the graph continues moving up to the right which means that the slope is positive. Therefore, graph (c) shows a changing acceleration $a_x$ that is always positive.